Major European river, second in length only to the Volga. It begins in the Black Forest in Germany, flows through Austria and Hungary, and forms the border of many of the Balkan countries before ending at the Black Sea in Romania. It flowed through the heartland of the La Tene culture, which produced the earliest Celtic artifacts (6th-5th c. BCE).

Ironically, the etymology of the name becomes "river river"--Danube < Danuvius < Old Celtic Danu-yo < IE danu- "the river," which is also name of the Irish goddess Danu, regarded as the mother of the gods; it is likely also related to the name of the Welsh goddess Dôn, also regarded as the mother of the gods. It is possible that the Danube was regarded as a sacred river by the Celts, so much so that the gods were the children of the goddess of this important river. Unfortunately, this is only speculation.